TST-2 (Tokyo Spherical Tokamak - 2) has been constructed
as an upgrade of the TST-M (Tokyo Spherical Tokamak -
Modified) device. On TST-M, experiments on helicity
injection and turbulence-induced transport have been carried
out with plasmas of relatively short pulse length (several
milliseconds) and low plasma current (60 kA). On TST-2, the
maximum flux capability of the ohmic coil will increase from
25mVs to 130 mVs and the toroidal field will increase from
0.3T to 0.4T. These changes will extend the plasma current
capability to about 0.2 MA and the discharge duration to
about 50 ms, enhancing the quality of discharge flat-top for
transport studies. However, the aspect ratio will be
restricted to a moderate value of 1.6 or higher. In addition
to continuing the research program of TST-M, radio frequency
(RF) experiments are planned.

TST-2 has a newly manufactured vacuum vessel that is
continuous in the toroidal direction. The vacuum vessel
consists of a 1.4 m diameter, 6 mm thick stainless steel
cylinder and top and bottom domes. The height of the vacuum
vessel is 1.5 m. The inner wall of the vacuum vessel is made
of a 0.23 m outer diameter, 1.6 mm thick Inconel-625 tube.
The new center stack consists of a 239-turn, double-layer
ohmic solenoid and the center legs of the 24-turn toroidal
field coil. The ohmic coil is designed to provide a flux
swing of 260 mVsec in the double-swing mode. Four pairs of
poloidal field coils are used for compensating the ohmic
leakage flux, production of the equilibrium field, and
creation of the poloidal field null during the breakdown
phase. The first plasma is scheduled in the summer of
1999.